This invention relates to a method for recovering heat energy from the exhaust gases of a big diesel engine provided with turbo apparatus and to an arrangement for implementing the method.
A "big diesel engine", as that term is used herein, means an engine suitable for an electricity generating plant or for a ship's power plant and the mechanical power output of which is, for instance, above 1 MW, even 20 MW or more. Such an engine is generally provided with a turbo apparatus driven by the exhaust gases for introducing charge air into the engine's cylinders. With an engine of this size it is often desired to make use of not only the mechanical energy generated by the engine but also the waste heat, or so-called secondary energy. For this purpose an exhaust gas boiler for heat energy recovery is generally mounted on the exhaust pipe of the engine right after the turbo apparatus. The temperature of the exhaust gases of a modern diesel engine, however, is relatively low, and the temperature falls further when passing through the turbo apparatus. Consequently, the heat exchanging surface of the exhaust gas boiler is quite large in relation to the heat energy to be recovered, and the exhaust gas boiler is large and costly. If the recovered heat energy is used for steam production, the relatively low temperature limits the pressure of the generated steam to about 4-16 bar, which corresponds to about 143.degree.-201.degree. C. for saturated steam.